I was testing this out myself pretty extensively and I use the following methods myself:
Safe) Units move in formation with guns down - face same direction
Aware) Units move in formation with guns always at ready - sometimes covering their "area" of view
Combat) Units move in formation by covering each other - leap frogging - tend to lag behind if leader runs ahead. They also tend to find cover behind trees, bushes, and walls that are nearby.
Stealth) Units move at their own pace trying to move from cover point to cover point. - hardly ever use formation and almost always go out of their way to find cover
I use aware when assaulting or evading. Keeps everyone in line and moving together. I use Combat once in combat and either holding position OR sometimes when moving forward in stages. I use Stealth when I move units to flank or when I want them to be smart about advancing forward into combat. Stealth also works well when you want to minimize exposure. Although I tend to think stealth has some unintended flaws and you need to keep an eye on your units as a safety precaution.
Stance is dependant on leader if you use the "Follow my stance" method. Even if units are in "Safe" mode, they will freak out and take cover if you drop to a prone position. Works well in the event of an ambush by enemy forces.
The other stances force the units to use only that stance. I never do this unless I am in battle and out gun the opposition.
Hold Fire works very well and I use it like 99% of the time with ground troops. Basically, they do not fire on targets unless they are fired at or you some form of a fire order. If done right, you can assign targets ahead of time and open fire for an ambush. Vehicle gunners tend to operate a bit differently with this command.
Corpsman (like: "Core men" said fast enough to sound like one word) :
http://encarta.msn.com/dictionary_1861600477/corpsman.html
